The present invention relates to ink jet printing. In particular, the invention relates to an inkjet printhead chip with predetermined micro-electromechanical systems height.
Many different types of printing have been invented, a large number of which are presently in use. Known forms of printers have a variety of methods for marking the print media with a relevant marking media. Commonly used forms of printing include offset printing, laser printing and copying devices, dot matrix type impact printers, thermal paper printers, film recorders, thermal wax printers, dye sublimation printers and ink jet printers both of the drop on demand and continuous flow type. Each type of printer has its own advantages and problems when considering cost, speed, quality, reliability, simplicity of construction and operation etc.
In recent years, the field of ink jet printing, wherein each individual pixel of ink is derived from one or more ink nozzles, has become increasingly popular primarily due to its inexpensive and versatile nature.
Many different techniques of ink jet printing have been invented. For a survey of the field, reference is made to an article by J Moore, xe2x80x9cNon-Impact Printing: Introduction and Historical Perspectivexe2x80x9d, Output Hard Copy Devices, Editors R Dubeck and S Sherr, pages 207-220 (1988).
Ink Jet printers themselves come in many different forms. The utilization of a continuous stream of ink in ink jet printing appears to date back to at least 1929 wherein U.S. Pat. No. 1,941,001 by Hansell discloses a simple form of continuous stream electro-static ink jet printing.
U.S. Pat. No. 3,596,275 by Sweet also discloses a process of a continuous ink jet printing including the step wherein the ink jet stream is modulated by a high frequency electrostatic field so as to cause drop separation. This technique is still utilized by several manufacturers including Elmjet and Scitex (see also U.S. Pat. No. 3,373,437 by Sweet et al)
Piezoelectric ink jet printers are also one form of commonly utilized ink jet printing device. Piezoelectric systems are disclosed by Kyser et. al. in U.S. Pat. No. 3,946,398 (1970) which utilizes a diaphragm mode of operation, by Zolten in U.S. Pat. No. 3,683,212 (1970) which discloses a squeeze mode of operation of a piezoelectric crystal, Stemme in U.S. Pat. No. 3,747,120 (1972) discloses a bend mode of piezoelectric operation, Howkins in U.S. Pat. No. 4,459,601 discloses a piezoelectric push mode actuation of the ink jet stream and Fischbeck in U.S. Pat. No. 4,584,590 which discloses a shear mode type of piezoelectric transducer element.
Recently, thermal ink jet printing has become an extremely popular form of ink jet printing. The ink jet printing techniques include those disclosed by Endo et al in GB 2007162 (1979) and Vaught et al in U.S. Pat. No. 4,490,728. Both the aforementioned references disclose ink jet printing techniques rely upon the activation of an electrothermal actuator which results in the creation of a bubble in a constricted space, such as a nozzle, which thereby causes the ejection of ink from an aperture connected to the confined space onto a relevant print media. Printing devices utilizing the electro-thermal actuator are manufactured by manufacturers such as Canon and Hewlett Packard.
As can be seen from the foregoing, many different types of printing technologies are available. Ideally, a printing technology should have a number of desirable attributes. These include inexpensive construction and operation, high-speed operation, safe and continuous long-term operation etc. Each technology may have its own advantages and disadvantages in the areas of cost, speed, quality, reliability, power usage, simplicity of construction operation, durability and consumables.
In the parent application, U.S. Pat. No. 6,416,167, there is disclosed a printing technology that is based on micro-electromechanical systems (MEMS) devices. In particular there is disclosed a printing mechanism that incorporates a MEMS device. There is also disclosed a method of fabricating such a mechanism.
The fabrication of MEMS devices is based on integrated circuit fabrication techniques. Very generally, a sacrificial material is deposited on a wafer substrate. A functional layer is then deposited on the sacrificial material. The functional layer is patterned to form a MEMS component. The sacrificial layer is then removed to free the MEMS component.
Applicant has found that topography of a MEMS chip is very important. The components are required to move. It follows that the topography must be such that sufficient clearance is provided for movement of the components. This means that such features as nozzle chambers must be deep enough to provide for functional movement of an actuator positioned in the nozzle chamber.
There are, however, problems associated with deep topography. This problem is illustrated in FIGS. A and B of the drawings. In FIG. A there is shown a substrate 1 with a layer of sacrificial material 2 positioned on the substrate 1.
One problem is immediately apparent. It is extremely difficult to achieve a uniform deposition on side walls 2 and a floor 3 of the cavity 4. The fluid dynamics of the deposition process is the primary reason for this. As a result, a portion of the sacrificial material within the cavity 4 tends to taper in to the side walls 2.
Accurate etching of the sacrificial material relies on a high image focus on the layer 2. It will be appreciated that this focus could be lost in the cavity 4, due to the depth of the cavity 4. This results in poor etching within the cavity 4.
Etching is carried out using a device that etches in steps. These are usually 1 micron in depth. It follows that each stepping process removes 1 micron of sacrificial material at a time. As can be seen in FIG. B, once a required part of the layer 2 has been removed, a part is left behind in the cavity 4. This is called a stringer 5. It will be appreciated that the stringer 5 is difficult to remove and is therefore an undesirable result.
The Applicant has conceived the present invention to provide a printhead chip that incorporates MEMS components that are spaced a predetermined distance from a wafer substrate so that sufficient ink ejection can be achieved. The predetermined distance is such that the chip topography avoids the problems described above.
According to a first aspect of the invention, there is provided a printhead chip for an inkjet printhead, the printhead chip comprising
a wafer substrate that incorporates drive circuitry, the wafer substrate defining a plurality of ink inlet channels; and
nozzle arrangements positioned on the wafer substrate, each nozzle arrangement comprising
a passive nozzle chamber structure that extends from the wafer substrate and bounds a respective ink inlet channel;
a dynamic nozzle chamber structure that, together with the passive structure, defines a nozzle chamber, and has a roof that defines the ink ejection port, the dynamic structure being displaceable towards the wafer substrate into an actuated position and away from the wafer substrate into a rest position such that a drop of ink can be ejected from the ink ejection port, and
an elongate micro-electromechanical actuator connected between the wafer substrate and the dynamic structure, the actuator including a beam assembly that has an active beam of a conductive material, capable of thermal expansion, that defines a heating circuit and is connected to the drive circuitry and a passive beam that is interposed between the active beam and the wafer substrate such that, when the active beam receives an electrical signal from the drive circuitry, the active beam expands relative to the passive beam driving the dynamic structure into the actuated position to generate the drop of ink and when the signal is cut off subsequent cooling of the active beam causes the dynamic structure to move back to the rest position, facilitating a separation of the drop of ink.
Each dynamic structure may include a skirt portion that depends from the roof inwardly of the passive structure, such that an edge of the skirt portion is proximate an edge of the passive structure in the rest position. The edges of the skirt portion and the passive structure may be configured so that, when the nozzle chamber is filled with ink, a meniscus is defined between the edges. The meniscus may define a fluidic seal as the active structure is displaced between the actuated and rest positions.
The edge of each skirt portion may be positioned between three and six microns above the wafer substrate, when the dynamic structure is in the rest position.
Each beam assembly may have an arm that interconnects the beams and the dynamic structure, so that displacement of the active and passive beams is transferred to the dynamic structure via the arm.
Each passive beam may be fixed, at one end, to the substrate, but insulated from the drive circuitry and fixed at an opposed end to the arm. Each active beam may be fixed, at one end, to the substrate to be electrically connected to the drive circuitry layer and also fixed at an opposed end to the arm.
Each passive beam and each passive structure may be of the same material.
According to a second aspect of the invention, there is provided an ink jet printhead chip that comprises
a wafer substrate,
a CMOS drive circuitry layer positioned on the wafer substrate, and
a plurality of nozzle arrangements positioned on the wafer substrate and the CMOS drive circuitry layer, each nozzle arrangement comprising
nozzle chamber walls and a roof wall that define a nozzle chamber and an ink ejection port defined in the roof wall, and
a micro-electromechanical actuator connected to the CMOS drive circuitry layer and that has at least one movable member that is positioned to act on ink in the nozzle chamber to eject the ink from the ink ejection port on receipt of a signal from the drive circuitry layer, the, or each, movable member being spaced between 2 microns and 15 microns from the CMOS drive circuitry layer.
The at least one movable member of each nozzle arrangement may be spaced between 5 microns and 12 microns from the CMOS drive circuitry layer. More particularly, the at least one movable member of each nozzle arrangement may be spaced between 6 microns and 10 microns from the CMOS drive circuitry layer.
The nozzle chamber walls and roof walls of each nozzle arrangement may be configured so that the nozzle chambers are generally rectangular in plan and transverse cross section. Each movable member may be planar and rectangular to extend across a length of its respective nozzle chamber. A free end of the movable member may be positioned between the CMOS drive circuitry layer and the ink ejection port. An opposed end of the movable member may be anchored to the CMOS drive circuitry layer. The movable member may incorporate heating circuitry that is electrically connected to the CMOS drive circuitry layer. The movable member may be configured so that, when the heating circuitry receives a signal from the CMOS drive circuitry layer, the movable member is displaced towards the ink ejection port as a result of differential expansion and, when the signal is terminated, the movable member is displaced away from the ink ejection port as a result of differential contraction.
Instead, the movable member may include an actuator arm of a conductive material that is configured to define a heating circuit that is connected to the CMOS drive circuitry layer and is configured to deflect towards the wafer substrate as a result of differential expansion when an electrical signal is received from the CMOS drive circuitry layer. The roof wall of the nozzle chamber and at least part of the nozzle chamber walls may be connected to the actuator arm, so that, when the actuator arm is deflected towards the wafer substrate, ink is ejected from the ink ejection port defined in the roof wall.
The invention extends to an ink jet printhead chip that includes a plurality of printhead chips as described above.
According to a third aspect of the invention, there is provided a method of fabricating an ink jet printhead chip having a wafer substrate, a CMOS drive circuitry layer positioned on the wafer substrate and a plurality of nozzle arrangements positioned on the wafer substrate and the CMOS drive circuitry layer, each nozzle arrangement having nozzle chamber walls and a roof wall that define a nozzle chamber and an ink ejection port in the roof wall and a micro-electromechanical actuator connected to the CMOS drive circuitry layer the actuator having at least one movable member that is positioned to act on ink in the nozzle chamber to eject the ink from the ink ejection port on receipt of a signal from the drive circuitry layer, the method comprising the steps of:
depositing between 2 microns and 15 microns of a first sacrificial material on the CMOS drive circuitry layer to define a deposition area for a layer of actuator material,
depositing said layer of actuator material on said deposition area,
etching the layer of actuator material to form at least part of each micro-electromechanical actuator, and
forming the nozzle chamber walls and roof wall by at least one of a deposition and an etching process.
The method may include the step of depositing between 5 microns and 12 microns of the first sacrificial material on the CMOS drive circuitry layer. In particular, the method may include the step of depositing between 6 and 10 microns of the first sacrificial material on the CMOS drive circuitry layer.
The step of forming the nozzle chamber walls and roof wall of each nozzle arrangement may include the steps of
depositing a second sacrificial material on the layer of actuator material to define a deposit area for at least part of the nozzle chamber walls and the roof wall,
depositing a structural material on the deposit area, and
etching the structural material to form the at least part of the nozzle chamber walls and the roof wall.